Chemical nickel plating processes and baths therefor



Feb. 4, 1958 G. GUTZEIT El AL CHEMICAL NICKEL PLATING PROCESSES ANDBATHS THEREFOR Original Filed Dec. 51, 1954 2 Sheets-Sheet 2 p m N M m wM m w 0 Z 4 0 H W 0 "Wm m B d g m u m M N M 0 0 M r P w r C 0 3 N M L 0,P1. 8% 3 E H Q3 Q3 2 0 4. 2 a 3 3 3 2 2 2 P. 2

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United States Patent Office 2,822,294 Patented Feb. 4, 1958 CHEMICALNICKEL PLATING PROCESSES AND BATHS THEREFOR Original applicationDecember 31, 1954, Serial No. 479,088. Divided and this applicationMarch 6, 1956, Serial No. 569,815

8 Claims. (Cl. 117-130) Paul Talmey, Barring- The present inventionrelates to improved processes of chemical nickel plating of catalyticmaterials employing baths of the nickel cation-hypophosphite anion typeand to improved baths therefor, and more particularly to such processesand baths involving a continuous system of the character of thatdisclosed in U. S. Patent No. 2,658,839, granted on November 10, 1953,to Paul Talmey and William J. Crehan. This application is a division ofthe copending application of Gregoire Gutzeit, Paul Talmey and Warren G.Lee, Serial No. 479,088, filed December 31, 1954; and the last-mentionedapplication is, in turn, a continuation-in-part of the copendingapplication of Gregoire Gutzeit, Paul Talmey and Warren G. Lee, SerialNo. 478,492, filed December 29, 1954.

The chemical nickel plating of a catalytic material employing an aqueousbath of the nickel cation-hypophosphite anion type is based upon thecatalytic reduction of nickel cations to metallic nickel and thecorresponding oxidation of hypophosphite anions to phosphite anions withthe evolution of hydrogen gas at the catalytic surface. The reactionstake place when the body of catalytic material is immersed in theplating bath, and the exterior surface of the body of catalytic materialis coated with nickel. The following elements are catalytic for theoxidation of hypophosphite anions and thus may be directly nickelplated: iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium,iridium and platinum. The following elements are examples of materialswhich may be nickel plated by virtue of the initial displacementdeposition of nickel thereon either directly or through a galvaniceffect: copper, silver, gold, beryllium, germanium, aluminum, carbon,vanadium, molybdenum, tungsten, chromium, selenium, titanium anduranium. The following elements are examples of non-catalytic materialswhich ordinarily may not be nickel plated: bismuth, cadmium, tin, leadand zinc. The activity of the catalytic materials varies considerablyand the following elements are particularly good catalysts in thechemical nickel plating bath: iron, cobalt, nickel and palladium. Thechemical nickel plating process is autocatalytic since both the originalsurface of the body being plated and the nickel metal that is depositedon the surface thereof are catalytic; and the reduction of the nickelcations to metallic nickel in the plating bath proceeds until all of thenickel cations have been reduced to metallic nickel, in the presence ofan excess of hypophosphite anions, or until all of the hypophosphiteanions have been oxidized to phosphite ions, in the presence of anexcess of nickel cations.

In a batch plating process, the reactions are sloweddown rather rapidlyas time proceeds because the anions, as contrasted with the cations, ofthe nickel salt that is dissolved in the plating bath combine with thehydrogen cations to form an acid, which, in turn, lowers the pH of thebath, and the reducing power of the hypophosphite anions is decreased asthe pH value of the bath decreases. Moreover, there is a tendency forthe early formation in the plating bath of a black precipitate thatcomprises a random chemical reduction of the nickel cations. Of

course, this formation of the black precipitate comprises adecomposition of the plating bath, and is particularly objectionable inthat it causes the nickel deposit to be coarse, rough and frequentlyporous. Any fine solid particles suspended in the plating bath, oradhering to the walls of the plating vessel, at the plating temperature,initiate the formation of the black precipitate by acting as nuclei.

In a continuous plating process the reactions aremaintainedsubstantially at their initial rates by the regeneration of the platingbath, i. e., by the adding thereto of soluble nickel-containing andhypophosphite-containing reagents, as well as an alkali for pH control;however, the problem of preventing the formation of black precipitate inthe plating bath and the consequent decomposition thereof is the same asthat previously mentioned. Moreover, another practical difficulty isencountered in the continuous plating process that is not encountered inthe batch plating process in that there is a considerable buildup of theby-product phosphite therein as time proceeds and as a consequence ofthe cycling of the bath. More particularly, while nickel hypophosphiteis readily soluble in an aqueous solution, nickel phosphite is much lesssoluble in an aqueous solution; whereby there is a tendency, as thephosphite concentration of the plating bath buildsup, for nickelphosphite to be precipitated therein, and thereby provide the solidparticles that serve as nuclei for the formation of the blackprecipitate therein, previously mentioned. In passing, it is noted thatthe initiationof the precipitation of nickel phosphite in the platingbath is indicated by turbidity thereof, visible in a Tyndall beam.

In carrying out the chemical nickel plating process on a commercialscale, the continuous system disclosed in the Talmey and Crehan patentmay be employed; which system involves periodic or continuousregeneration of the plating bath by the addition thereto of appropriateingredients for the purpose of maintaining substantially constant thecomposition of the bath, as previously noted. More specifically in thissystem, there are provided a plating chamber and a reservoir; preferablyone portion of the plating solution is stored at a relatively lowtemperature well below the boiling point thereof in the reservoir; andpreferably another portion of the plating solution is held as a bath ata relatively high temperature slightly below the boiling point thereofin the plating chamber. The solution is continuously circulated at a lowrate from the reservoir to the plating chamber and then back to thereservoir, the solution being heated substantially to the relativelyhigh temperature after withdrawal thereof from the reservoir and beforeintroduction thereof into the plating chamber, and the solution beingcooled substantially to the relatively low temperature after withdrawalthereof from the plating chamber and before return thereof to thereservoir. The body that is to be nickel plated is immersed in the bathin the plating chamber and is subsequently withdrawn from the bath inthe plating chamber after a time interval corresponding to the thicknessof the nickel plating thereon that is desired; and during such timeinterval soluble reagents are added to the solution in the reservoir tomaintain in the bath in the plating chamber during such time intervalsubstantially the predetermined composition of the bath previouslymentioned, so as to compensate for the ingredients of the bath that areexhausted during the time interval in the plating chamber. Thisregeneration of the solution in the reservoir consists essentially ofadding thereto appropriate amounts of soluble nickel-containing andhypophosphite-containing reagents, as well as analkali for pH control,as previously noted.

In a plating bath of the nickel cation-hypophosphite anion type, thethreshold of precipitation of the insoluble nickel phosphite begins whenthe (HPO concentration attains a value above the solubility of itssimple nickel salt or its double nickel-alkali salt; i. e., above 0.03to 0.07 m. p. 1.; and in order to obviate this defect, there aredisclosed in the c'opending application of Gutzeit, Talmey and Lee,Serial No. 478,492, modified plating baths of the nickelcation-hypophosphite anion type containing both complexing agents andexalting additives. In these plating baths, the complexing agents serveto tie-up the nickel ions, thereby preventing precipitation of nickelphosphite until a high concentration of phosphite ions (about 1.0 m. p.l.) is reached in the plating bath in the continuous plating system; andthe exalting additives serve to increase the normally low plating ratesof these baths containing the complexed nickel ions. Among thecomplexing agents disclosed, those forming water-soluble chelates aremost efiicien t; and, within that group, the hydroxycarboxylic acidshave several practical advantages, such as: ready availability, lowprice and high buffering capacity.

More particularly, it is apparent that if the nickel ions are verystrongly tied-up (i. e., if the chelate is very stable), they areactually removed from the plating process, and no longer available fordeposition; whereas, if the complex bond energy is at a lower level, anequilibrium is reached between the dissociation rate of the nickelcomplex ion and the deposition rate of metallic nickel. The stability ofnickel chelates with various hydroxycarboxylic acid additives is notonly a function of the number of hydroxyl and carboxyl groups in theacid molecule, but also of molecular structure and steric factors, asmay be better appreciated from a consideration of the structure of themore common of these acids:

Glycollic acid (hydroxyacetic acid) Hip-00011 H Malic acid(monohydroxysuc'cinic acid) H2 00'0H Lactic acid (alpha-hydroxypropionicacid) CH3 ire-AH GOOH Tartaric acid (dihydroxysuccinic acid) 11 'mz-ooon HO-GO0H Citric acid H:CCOOH BIO- -000H H: CO0H It is obvious thattartaric acid having two hydroxyl and two carboxylgroups will give themost stable complex; and it is also normal that glycollic and lacticacid complexes will show the least stability, both beingmonohydroxy-monocarboxylic acids. On the other hand, the lactic chelateof nickel is less stable than the glycollic complex; and this is due toa structural factor, i. e., the presence of an additional methyl group(CI-l Moreover, chelate stability is also determined by the number ofcarboxyl groups in the molecule so that the nickelmalic acid complex (amonohydroxy-dicarboxylic compound) is more stable than the correspondingchelates of both glycollic and lactic acids (monohydroxy-monocarboxylicacids), while the citric acid complex is them stable of all.

. Generally, if hydroxycarboxylic acids (instead of a non-chelatingbutler) are added to a chemical plating bath of the nickelcation-hypophosphite anion type in continuous operation, the resultingplating rate will be an inverse function of chelate stability; however,on the other hand, the more stable the nickel complex, the higher aphosphite ion concentration can be built up before precipitation ofnickel nhosnhite occurs.

For the above reasons, the plating baths disclosed in the Gutzeit,Talmey and Lee application, Serial No. 478,492, comprise relativelystable complexing agents in combination with powerful exaltingadditives, dicarboxylic acids, aminocarboxylic acids and certainmonocarboxylic acids (to increase the normally low plating rates ofthese baths).

The present invention is predicated upon the discovery that in a platingbath of the nickel cationhypophosphite anion type described, while thenickel chelating function of lactic acid is directly proportional to theconcentration thereof in the bath, the effect thereof upon the platingrate of the bath is not inversely proportional to the concentrationthereof (as is the general case with the other hydroxycarboxylic acids);rather within a given range of concentration, lactic acid is a definiteexaltant in the bath, substantially increasing the plating rate thereof,together with the discovery that in the utilization of propionic acid asan exaltant in these lactic acid complexed plating baths synergisticexalting elfects are produced. The mechanism of these exalting efiectsis not fully understood, but these effects are very pronounced; and aremost unusual and entirely unexpected.

The general composition of a plating bath, in accordance with thepresent invention, essentially comprises an aqueous solution of a nickelsalt, a hypophosphite, lactic acid or a salt thereof, and propionic acidor a salt thereof; wherein the absolute concentration of hypophosphiteanions in the bath is in the range 0.15 to 1.20 m. p. 1., the ratiobetween nickel cations and hypophosphite anions in the bath expressed inmolar concentration is within the range 0.25 to 1.60, the absoluteconcenration of lactic anions in the bath is in the range 0.25 to 0.45m. p. 1., and the absolute concentration of propionic anions in the bathis within the range 0.025 to 0.045 m. p. l. The pH of the bath isnormally in the range 4.0 to 5.6; and the bath is employed in theplating chamber of the continuous plating system at a'temperature aboveC., ordinarily slightly below the boiling point thereof and at about 97to 99 C. The bath has a nickel plating rate of at least 1 mil/hour(0.001"/hour), or expressed in c. g. s. units, of at least 3.5 X l0gm./crn. /min.; and no precipitation of nickel phospln'te takes placetherein even at a phosphite ion concentration in some cases very closeto 1.0 m. p. 1. Further, the plating appearance on both metals andnon-metals is excellent (bright, smooth and non-porous); and adhesion ofthe nickel plating on both metallic and non-metallic bodies is excellent(no flaking of the nickel coating in bending, abrading and shock tests).

In accordance with the process of the present invention, the platingbath of the composition specified is preferably employed in thecontinuous plating system of the character previously described, wherebythe lactic acid additive is present therein in the optimum rangespecified so that it serves both the complexing or chelating functionwith respect to the nickel ions and also the function of increasing theotherwise relatively low plating rate of the bath, and whereby thepropionic acid additive is present therein in the optimum rangespecified so that it serves the function of further increasingdisproportionately the plating rate of the bath. This complexing of thenickel cations'in the plating bath prevents the formation ofprecipitated phosphite therein, thereby rendering the bath ofexceedingly long life in spite of the build-up of phosphite ions thereinto a concentration even in excess of 1 molar. This complex of nickel inthe plating bath is water-so1uble and of medium stability resulting in,a bond strong enough to prevent the nickel cations from forminginsoluble nickel compounds, but having a stability constant low enoughto release the nickel cations required for the nickel plating operationto efiect a plating rate of the bath of at least 3.5 l0 gm./cm. /min.,as previously explained.

In view of the foregoing, it is the primary object of the presentinvention to provide an improved nickel plating process of the characterdescribed in which the reactions involved are carried out moreefliciently and under more stable conditions (clarity of solution) thanheretofore, thereby rendering the process more desirable from acommercial standpoint.

Another object of the invention is to provide an improved aqueouschemical nickel plating bath that may be employed with advantage in thepractice of the improved process.

Another object of the invention is to provide an improved nickel platingprocess of the character described, that employs a plating bath of thenickel cation-hypophosphite anion type of the character specified,wherein the lactic acid substantially completely complexes all of thenickel cations in the bath, and wherein the combination of the lacticacid and the propionic acid substantially increases the plating ratethereof to at least 3.5 X gm./cm. /min.

A further object of the invention is to provide an improved nickelplating process of the continuous type involving an improved platingbath of the nickel cationhypophosphite anion type, so that the usefullife of the bath is greatly extended in that it remains clear,notwithstanding the presence therein of a phosphite anion concentrationapproaching 1 molar.

A still further object of the invention is to provide an improved nickelplating bath of the character described that involves the combination ofa novel range of lactic ion addition and a novel range of propionic ionaddition.

These and other objects and advantages of the invention pertain to theparticular arrangement of the steps of the plating process and of thecomposition of the plating bath, as will be understood from theforegoing and following description taken in connection with theaccompanying drawings, in which:

Figure l is a curve illustrating the relationship between p'hosphitetolerance of a plating bath of the type described and the concentrationof lactic acid contained therein;

Fig. 2 is two curves illustrating the relationship between phosphitetolerances of two plating baths of the type described and the pHthereof;

Fig. 3 is a curve illustrating the relationship between the plating rateof a plating 'bath of the type described and the pH thereof; and

Fig. 4 is two curves illustrating the relationship between the platingrates of the two plating baths of the type described and theconcentration of phosphite therein.

In accordance with the process of the present invention, the article tobe nickel plated and norm-ally having a catalytic surface is preferablyprepared by mechanical cleaning, degreasing and light picklingsubstantially in accordance with standard practices in electroplatingprocesses. For example, in the nickel plating of a steel article, it iscustomary to clean the rust and mill scale from the article, to degreasethe article and then lightly to pickle the article in a suitable acid,such as hydrochloric acid. The article is then immersed in a suitablevolume of the plating bath containing the proper proportions of nickelcations, hypophosphite anions, lactic ions and propionic ions, the pH ofthe bath having been, if necessary, adjusted to an optimum value by theaddition of an appropriate acid or base, and the bath having been heatedto a temperature just below its boiling point,

such as 99 C. at atmospheric pressure. Almost immediately, hydrogenbubbles are'formed on the catalytic surface of the steel article andescape in a steady stream from the plating bath, while the surface ofthe steel article is slowly coated with metallic nickel (containing somephosphorus). The steel article is subsequently removed from the bathafter an appropriate time interval corresponding to the requiredthickness of the nickel coating deposited thereon that is desired; andultimately the steel article is rinsed 0E with water, so that it isready for use.

In the plating'bath, the nickel cations may be derived from nickelchloride, nickel sulfate, etc., or various combinations thereof; thehypophosphite anions may be de rived from sodium hypophosphite,potassium hypophosphite, etc., or various combinations thereof; thelactic ions may be derived from lactic acid, or various lactates, orvarious combinations thereof; and the propionic ions may be derived frompropionic acid, or various propionates, or various combinations thereof.The desired pH of the bath is established by the eventual introductionthereinto of a suitable acid, such as hydrochloric acid, sulfuric acid,etc., or an alkali such as sodium hydroxide, sodium carbonate, sodiumbicarbonate, etc.

The terms cation, anion and ion as employed herein, except wherespecifically noted, include the total quantity of the correspondingelements that are present in the plating bath, i. e., both undissociatedand dissociated material. In other words, 100% dissociation is assumedwhen the terms noted are used in connection with molar ratios andconcentrations in the plating bath.

In order to demonstrate the remarkable advantages ,of the plating bathsof the present invention, several series of plating tests were conductedemploying standard steel samples that had been given a standardpre-treatment. More particularly, steel samples (Dayton Rodgers) of 20cm. total area were vapor degreased, cleaned by an alkaline soak andlightly pickled in 1:1 hydrochloric acid. The steel samples thusprepared were then plated at 98i C. in 50 cc. of different plating bathsin 10-minute tests and involving a plating bath of the followingfundamental composition:

BATH I Nickel ion (as nickel sulfate)"; m. p. l-.. 0.08 Hypophosphiteion (as sodium hypophosph lte -m. p. 1... 0.225 Lactic ion (as lacticacid) m. p. l 0.30

Utilizing plating Bath I containing various ones of the exaltantsindicated, the following results were obtained, as set forth in thetable below:

1 Bright and smooth.

Again utilizing plating Bath I, steel samples (pretreated in the mannerpreviously explained) were plated in 60-minute tests, the plating bathcontaining various ones of the exaltants indicated, and with the resultsset forth in the table below:

From a comparison of'Tables IA and IE, it will be appreciated thatpropionic acid is a far better exaltant in the -minute rate test thanthe other soluble short chain aliphatic monocarboxylic acids, but thatit is somewhat inferior in this regard to acetic acid in the 60- minutetest. Nevertheless, propionic acid represents the preferred,exaltantbecause acetic acid is easily volatilized, particularly throughsteam entrainment, and butyric acid and valeric acid are more expensive.Moreover, propionic acid is preferred for the additional reason that thestructure thereof is quite similar to that of lactic acid, since lacticacid is of course alpha-hydroxypropion'ic acid. In these plating baths,the quantity of propionic anion required as an'exalting additive isabout 10% of that of thelactic anions required as a complexing agent;whereby the ration Ni++/propionic anion should be preferably tate. Thecalcium salts of propionic, butyric and Valerie acids satisfy thiscondition, as do the calcium salts of lacticracidi At this point, it ismentioned that most common hydroxycarboxylic acids (malic, citric,tartaric, etc.) form insoluble calcium compounds.

In the continuous plating system, a similar plating test was performedinvolving a number of cycles of circulation of the body of platingsolution and including periodic regeneration of the plating bath in thereservoir exteriorly of the plating chamber, as disclosed in thepreviously mentioned 'Talmey and Crehan patent. In this plating test, anumber of cold rolled steel samples (1%" x 6" x 14 ga.) were employedthat had been subjected to a pretreatment including vapor degreasing,alkaline soaking and pickling in 2:1 hydrochloric acid. In this platingtest, the initial composition of the plating bath was as follows:

with caustic soda; and the specific results of this continuous platingtest are set forth in the table below:

Table II Cycle No 1 2 3 4 5 6 7 8 9 10 Total weight gain (gm.) 6- 05 5.6 6.1 5. 6 6. 0 2. 95 2. 90 3. 2.90 2.70 Plating rate, R X10(gmJcrnfl/mrn). 3. 31 3. 3.19 3.45 3. 34 4. 00 3. 84 3. 61 3. 78 3. 65Plating rate (mil/1m)--- 0. 94 0.99 0. 91 0.99 0. 95 1. 14 1.10 1.031.08 1. 04 Solution flow rate (co/1n 100 100 100 100 100 100 100 100 100I 100 Plating time (121111.) 63 55 66 56 62 52 63 53 51 I itial pH 4. 704. 58 4.60 4. 7o 4. s5 4. so 4. 52 4.50 4. 50 4. 50 N1 added (gm. asNlSO4-6Ha0) 5. 6 5. 2 5. 7 5. 2 5. 6 2.70 2. 69 3. 10 2. 69 2. 50NaHzPOq added (gm) 30 28 31 30 30 15 15 17 15 14 N aQH added (gm.) 7. 13.6 3. 6 4. 2 3. 6 3. 4 Additive (p p. 111.) Pl) 1 5 0 0. 5 0. 5 0 0. 50 Ni turnover (mol/l.). 0742 0.0820 0.0895 0. 0984 O. 1060 0.1130 Platmgappearance 0) 0) 0) '(l 1 Bright and smooth.

in the approximate range 1.5 to 2.5, since the Ni++/ lactic anion shouldpreferably be in the approximate range 0.15 to 0.25. However, the bathmay contain propionic anions in the approximate range 0.025 to 0.060 m.p. 1., since it may contain lactic anions in the approximate range 0.25to 0.60 m. p. 1.

In plating operations involving plating baths of the nickelcation-hypophosphite anion type containing lactic ion as the complexingand exalting agent, the utilization of the simple short chain saturatedmonocarboxylic acids (propionic, butyn'c and valeric) is mostadvantageous in view ofthe solubility of the calcium salts thereof. Morespecifically, in the operation of the continuous plating system, after arelatively long time interval of pro duction plating, the phosphiteconcentration builds up to a point where a slight excess of (HPO despitethe presence of a complexing agent, will result in nickelphosphiteprecipitation; in other words, a threshold isreached wherethesolubility of nickel phosphite, even in the presence of a nickelchelating agent, is exceeded. At this time, it becomes necessary toremove, by some method, the excess phosphite ion, as well as the excesssodium and sulfate ions that have accumulated as the result ofregeneration. A simple and economical method ofachieving this objectiveis disclosed in the copending application of Paul Talmey, GregoireGutzeit and Donald E. Metheny, Serial No. 479,040, filed December 31,1954, and involving the addition to the spent plating bath of a slightexcess of calcium hydroxide, resulting in the precipitation of nickelphosphite, calcium phosphite and calcium sulfate; whereby, vforpractical reasons/it is highly desirable :to employ in .these plating.baths .an exaltant which is' not removed ;in.the '.-.above. describedprocess, its calcium salt being soluble as is calcium lac- Incycles 1to'S, inclusive, of this plating test, two of the panels specifiedhaving a total area of 290 cm. were plated; whereas in cycles6 to 10',inclusive, of this plating test, only one panel specified having a totalarea of cm. wasplated. In this plating test, the quality of the platingwas excellent, particularly with respect to smoothness, lack of porosityand corrosion-resistance.

The phosphite tolerance of these plating baths of the nickelcation-hypophosphite anion type (also containing both lactic acid andpropionic acid) is dependent substantially upon the concentration oflactic acid in the bath.

For example, a plating bath of this type was tested that had thefollowing composition:

The results of these tests are set forth in the table below:

Table III Lactic ion Phosphite (m; vp. l.) tolerance (to. p. l.)

The results of these tests are also illustrated graphical: ly by thecurve 11 in Fig. l; and it is noted that the phosphite tolerance ofthese baths is established substantially by the concentration of lacticacid therein. Also it will appear from the curve 11 of Fig. 1 that it isadvantageous to use Bath III at the highest possible lactic ionconcentration (consistent with good plating) in order to give theplating bath a long life in use. On the other hand, an increase in thelactic acid concentration above about 0.4 m. p. l. at substantiallyconstant pH results in a marked decrease of the plating rate of aplating bath of this type.

This was demonstrated by a series of -minute plating tests employingsteel samples (pretreated in the manner previously explained) and usinga plating bath having the following composition:

BATH IV NiSo .6H O m. p. l 0.08 Na(I-I PO m. p. 1 0.225 Propionic acidm. p. l 0.03 Lactic acid variable Initial ph 4.6

The results of these plating tests are set forth in the table below:

Table IV Lactic acid (m. p. 1.) 0.10 0.20 0. 30 0. 40 0.50 Averageplating rate (gm./

emfi/mmxloo s. 700 3.730 3.585 3.585 3.260 Final pH 3. 90 4.00 4.15 4.204.30

The plated samples were smooth and semi-bright; and it is noted that thefinal pH decreased from the initial pH in a manner inverselyproportional to the lactic acid concentrations in the plating baths as aresult of the buffering effect of the lactic acid.

From Table IX, it is apparent that the optimum lactic anionconcentration in plating Bath IV (at a pH of 4.6) is about 0.4 m. p. 1.giving this plating bath a phosphite tolerance of 1.4 m. p. 1. In theuse of the plating bath, if the plating rate can be sacrificed, a higherlactic anion concentration (for instance 0.5 m. p. 1.) can be usedtherein in order to achieve an overall saving in chemicals.

If the pH of a plating bath of this type is changed, the phosphitetolerance increases with increasing hydrogen ion concentration; however,the plating rate also decreases as the pH of the plating bath islowered.

In order to demonstrate these facts, two plating baths were tested thathad the compositions set forth below:

Lactic anion0.40 m. p. l

The results of these tests are respectively set forth in the tablesbelow:

Table V Lactic anion0.30 m. p. 1.

pH Phosphlte tolerance .10 Table VI Lactic anion 0.40 m. p. 1.

Phosphite tolerance From a comparison of the results of these testsrespectively set forth in Tables V and VI, and respectively employingplating Baths V and VI, it will be appreciated that the phosphitetolerance of a plating bath of this type is increased both with anincrease in the concentration of lactic anion and with a decrease in thepH thereof.

The results of these tests are also illustrated graphically by therespective curves 21 and 22 in Fig. 2.

In order to demonstrate the effect of pH variations upon the platingrate of a plating bath of this type, a: series of 10-minute platingtests were run employing steel samples of the character previouslydescribed and utilizing a bath of the composition set forth below:

The results of these plating tests are set forth in the table below:

Table VII pH 4. 70 4.60 4.50 Average plating rate (gm./cm. /min. 10 3.352. 94 2. 89

The results of these plating tests are also graphically illustrated bythe curve 31 in Fig. 3.

Actually the matter of selecting the range of the lactic anionconcentration and the pH of a plating bath of this character dependsupon an economic problem in that a high phosphite tolerance lowers thecost of the chemicals per unit surface area nickel plated, while a highplating rate lowers the labor cost and amortization of the plantequipment. For practical purposes, a pH between 4.5 and 4.7 appears tobe most desirable.

Further, it is pointed out that while a high phosphite tolerance isadvantageous as noted above, the plating rate of a bath containing ahigh phosphite concentration is also impaired. This was demonstrated intwo series of 10-minute plating tests that were run employing steelsamples prepared in the manner previously explained and utilizing twobaths having the compositions indicated below:

Identical to Bath VIII except that it contains:

Lactic anion-0.4O m. p. l.

The results of these plating tests are respectively set forth in thetables below:

Table VIII Lactic anion-0.30 m. p. I.

Phosphite concentration (m. p. l.)

10 Average plating rate (gm./cm. /mtn'.X10).--.

Table IX Lactic anion-0.40 in. p. l.

The results of these plating tests are also illustrated graphically bythe curves 41 and 42. in Fig. 4.

Thus it will be appreciated that as the phosphite conconcentrationbuilds up in a plating bath of this type, as the plating bath is used inthe continuous plating system, the plating rate of the bath declines.Accordingly, it will be appreciated that the level of concentration ofthe phosphite'in a plating bath of this type must be maintained as lowas possible by employing continuous regeneration thereof during use, asdisclosed in the previously-mentioned copending application of PaulTalmey, Gregoire Gutzeit and Donald E. Metheny. Otherwise, the platingbath must be discarded for further use, when about one-half tothree-fourths of the phosphite tolerance thereof is reached, thereby toinsure that in the plating operation, there is no formation of blackprecipitate in the plating bath.

in view of the foregoing, it is apparent that there has been provided animproved, process of chemical nickel plating, as well as improvedplating baths therefor, wherein the baths are of the nickelcation-hypophosphite anion, type, and containing as a combinationcomplexing agent and exalting additive a predetermined range of lacticacid and containing as a separate and independent exalting additive asimple short chain saturated aliphatic monocarboxylic acid, preferablypropionic acid. These plating baths are particularly well-adapted foruse in a continuous plating system, as they exhibit a fast plating rate,have an exceedingly long life, are productive of entirely satisfactoryplating quality, and maintain nickel phosphite in solution inconcentrations approaching one molar.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein, and it is intended to coverin the appended claims all such modifications as fall within the truespirit and scope of the invention.

Whatis claimed is:

l. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum,which comprises contacting said body with a bath consisting essentiallyof an aqueous solution of nickel ions, hypophosphite ions, 21 complexingagent selected from the group consisting of lactic acid and saltsthereof, and an exalting additive selected from the group consisting ofsimple short chain saturated aliphatic monocarboxylic acids including 3to 5 carbon atoms and salts thereof, wherein the absolute concentrationofhypophosphite ions in said bath expressed in mole/liter is within therange 0.15 to 1.20, the ratio between nickel ions and hypophosphite ionsin said bath expressed in molar concentrations is within the range 0.25to 1.60, the absolute concentration of lactic ions in said bathexpressed in mole/liter is within the range 0.25 to 0.60, and theinitial pH of said bath is within the approximate range 4.4 to 5.6.

2. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum,which comprises contacting said body with a bath consisting essentiallyof an aqueous solution of nickel ions, hypophosphite ions, a complexing.a-gcnt selected from the group consisting of lactic acid and saltsthereof, and an exalting additive selected from the group consisting ofpropionic acid and salts thereof, wherein the absolute concentration.-ofhypophosphite-ions in said bath expressed in mole/liter is within therange 0.15 to 1.20, the ratio between nickel ions and hypophosphite ionsin said bath expressed in molar concentrations is within the range 0.25to 1.60, the absolute concentration of lactic ions in said. bathexpressed in mole/liter is within the range 0.25 to. 0.60, and theinitial pH of said bath is within the approximate range 4.4 to 5.6.

3. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum,which comprises contacting said body with a bath consisting essentiallyof an aqueous solution of nickel ions, hypophosphite ions, a complexingagent selected from the group consisting of lactic acid and saltsthereof, and an exalting additive selected from the group consisting ofpropionic acid and salts thereof, wherein the absolute concentration ofhypophosphite ions in said bath expressed in mole/liter is within therange 0.15 to 1.20, the ratio between nickel ions and hypophosphite ionsin said bath expressed in molar concentrations is within the range of0.25 to 1.60, the absolute concentration of lactic ions in said bathexpressed in mole/literis within the range 0.25 to 0.60, the absoluteconcentration of propionic ions in said bath expressed in mole/liter iswithin the range 0.025 to 0.060, and the initial pH of said bath iswithin the approximate range 4.4 to 5.6.

4. The process, of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, coper, silver, gold, palladium and platinum,which comprises contacting said body with a bath consisting essentiallyof an aqueous solution of nickel ions, hypophosphite ions, a complexingagent selected from the group consisting of lactic acid and saltsthereof, and an exalting additive selected from the group consisting ofpropionic acid. andsalts thereof, wherein the absolute concentration ofhypophosphite ions in said bath expressed in mole/liter is within therange 0.15 to 0.35, the ratio between nickel ions and hypophosphite ionsin said bath expressed in molar concentrations is within the range 0.25to 0.60, the absolute concentration of lactic ions in said bathexpressedin mole/liter is within the range 0.25 to 0.45, the absoluteconcentration of propionic ions in said bath expressed in mole/liter iswithin the range 0.025 to 0.045, and the initial pH of said bath iswithin the approximate range 4.5 to 4.7.

5'. A bath for the chemical plating of a catalytic material with nickelconsisting essentially of an aqueous solution of a nickel salt, ahypophosphite, a complexing agent selected from the group consisting oflactic acids and salts thereof, and an exalting additive selected fromthe group-consisting of propionic acid and salts thereof, wherein theabsolute concentration of hypophosphite ions in said bath-expressed inmole/liter is within the range 0.15 to 1.20, the ratio between nickelions and hypophosphite ions in said bath expressed in molarconcentrations is within the range 0.25 to 1.60, the absoluteconcentration of lactic ions in said bath expressed in mole/liter iswithin the range 0.25 to 0.60, the absolute concentration of propionicions in said bath expressed inmole/liter is within the range 0.025 to0.060, and the initial pH of said bath is within the approximate range4.4 to 5.6. i

6. The process of chemically plating with nickel a body essentiallycomprising anelement selected from the group consisting of iron, cobalt,nickel, aluminum, copper, silver, gold, palladium and platinum, whichcomprises contacting said body with a bath consisting essentially of anaqueous solution of nickel ions, hypophosphite ions, a complexing agentselected from the group consisting of lactic acid and salts thereof, andan exalting additive selected from the group consisting of simple shortchain saturated aliphaticmonocarboxyl ic acids including 3 to 5 carbonatoms and salts thereof, wherein the absolute concentration ofhypophosphite ions in said bath expressed in mole/liter is within therange 0.15 to 1.20, the ratio between nickel ions and hypophosphite ionsin said bath expressed in molar concentrations is within the range 0.25to 1.60, the absolute concentration of lactic ions in said bathexpressed in mole/liter is within the range 0.25 to 0.45, and theinitial pH of said bath is Within the approximate range 4.4 to 5.6.

7. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum,which comprises contacting said body with a bath consisting essentiallyof an aqueous solution of a nickel salt, a hypophosphite, a complexingagent selected from the group consisting of lactic acid and saltsthereof, and an exalting additive selected from the group consisting ofpropionic acid and salts thereof, wherein the absolute concentration ofhypophosphite ions in said bath expressed in mole/liter is within therange 0.15 to 1.20, the ratio between nickel ions and hypophosphite ionsin said bath expressed in molar concentrations is within the range 0.25to 1.60, the absolute concentration of lactic ions in said bathexpressed in mole/liter is within the range 0.25 to 0.45, the absoluteconcentration of propionic ions in said bath expressed in mole/liter iswithin the range 0.025 to 0.045, and the initial pH of said bath iswithin the approximate range 4.4 to 5.6.

8. The process of chemically plating with nickel a body essentiallycomprising an element selected from the group consisting of iron,cobalt, nickel, aluminum, copper, silver, gold, palladium and platinum,which comprises contacting said body with a bath consisting essentiallyof an aqueous solution of nickel ions, hypophosphite ions, lactic ionsand propionic ions, wherein the absolute concentration of hypophosphiteions in said bath expressed in mole/liter is within the range 0.15 to1.20, the ratio between nickel ions and hypophosphite ions in said bathexpressed in molar concentrations is within the range 0.25 to 1.60, theabsolute concentration of lactic ions in said bath expressed inmole/liter is at least about 0.25, and the absolute concentration ofpropionic ions in said bath expressed in mole/liter is at least about0.025.

No references cited.

1. THE PROCESS OF CHEMICALLY PLATING WITH NICKEL A BODY ESSENTIALLYCOMPRISING AN ELEMENT SELECTED FROM THE GROUP CONSISTING OF IRON,COBALT, NICKEL, ALUMINUM, COPPER, SILVER, GOLD, PALLADIUM AND PLATINUM,WHICH COMPRISES CONTACTING SAID BODY WITH A BATH CONSISTING ESSENTIALLYOF AN AQUEOUS SOLUTION OF NICKEL IONS, HYPOPHOSPHITE IONS, A COMPLEXINGAGENT SELECTED FROM THE GROUP CONSISTING OF LACTIC ACID AND SALTSTHEREOF, AND AN EXALTING ADDITIVE SELECTED FROM THE GROUP CONSISTING OFSIMPLE SHORT CHAIN SATURATED ALIPHATIC MONOCARBOXYLIC ACIDS INCLUDING 3TO 5 CARBON ATOMS AND SALTS THEREOF, WHEREIN THE ABSOLUTE CONCENTRATIONOF HYPOPHOSPHITE IONS IN SAID BATH EXPRESSED IN MOL/LITER IS WITHIN THERANGE 0.15 TO 1.20, THE RATION BETWEEN NICKEL IONS AND HYPOPHOSPHITEIONS IN SAID BATH EXPRESSED IN MOLAR CONCENTRATIONS IS WITHIN THE RANGE0.25 TO 1.60, THE ABSOLUTE CONCENTRATION OF LACTIC IONS IN SAID BATHEXPRESSED IN MOLE/LITER IS WITHIN THE RANGE 0.25 TO 0.60, AND THEINITIAL PH OF SAID BATH IS WITHIN THE APPROXIMATE RANGE 4.4 TO 5.6.